A key question in cellular physiology concerns the molecular determinants of receptor properties. In this study chemical modifications of sulfhydryl groups on the cholinergic receptor at the neuromuscular junction will be used to study receptor specificity, affinity and translation of agonist binding into conductance of ionic channels. It had been thought that the oxidation state of a particular disulfide group of a cystine residue on the cholinergic receptor was a determinant of these receptor properties. I have recently shown that charge at this locus is also an important factor. I now propose further modifications at this sight and more comprehensive analysis of receptor function. I will use standard electrophysiological techniques to measure receptor affinity, specificity and single channel conductance parameters before and after addition of specific chemical groups to a sulfhydryl locus near the acetylcholine binding site on the receptor. These groups will differ in charge and in steric factors and their effect on receptor properties will be used to deduce structural determinants of receptor function.